International Patent Application Number PCT/US02/36901, filed Nov. 14, 2002 and published in English on May 22, 2003 as WO 03/041660 A2 discloses toposiomerase poisons of formula XX:
that are reported to have inhibitory activity against topoisomerase I and/or topoisomerase II and to displayed anticancer activity. In spite of this disclosure, there is currently a need for agents that have an increased therapeutic window, fewer side effects, increased activity, and/or better pharmacokinetic properties, such as bioavailability or enhanced cell or tissue targeting.